1. Field of the Invention
The invention relates to a pneumatic tool (or compressed air tool), and more specifically, to an air filter unit capable of preventing infiltration of foreign matter into the pneumatic tool.
2. Description of the Related Art
In a pneumatic tool to which compressed air is supplied through a hose from a compressed air supply source such as an air compressor, foreign matter such as sand and dust sometimes infiltrates into a socket when the hose is removed from the socket of the pneumatic tool. If the pneumatic tool with the sand and the like infiltrated into the socket is operated by connecting the hose to the pneumatic tool, the sand and the like may, in some cases, clog a trigger valve or enter into a cylinder to cause such abnormality as defective operation of a piston and the like. Thus, a pneumatic tool with an air filter unit has been proposed in order to prevent the infiltration of foreign matter into an air chamber of the pneumatic tool.
The air filter unit of this pneumatic tool will be described with reference to FIG. 3. FIG. 3 shows a nail gun 1. A body 2 of the nail gun 1 is formed by integrally molding a mechanical part housing 3 and a grip 4. An end cap 5 is fitted into the opening on the end of the hollow grip 4 with a bolt 6. A hose connector plug 8 is attached to a compressed air supply port 7 that is opened through along the center of the end cap 5, so that compressed air is supplied to an air chamber within the body 2 by connecting an air compressor (not shown) to the hose connector plug 8 through a hose.
An air filter 9 is attached to the surface on which the grip 4 comes in contact with the end cap 5 so as to be interposed between the grip 4 and the end cap 5. The air filter 9 has a slightly larger diameter than that of the grip 4 or of the end cap 5. The air filter 9 is formed sheetlike by compressing synthetic fibers or the like, and filters the compressed air flowing into the compressed air supply port 7 before the compressed air is supplied to the air chamber.
In the conventional air filter unit that is formed by attaching the sheetlike air filter within the grip of the pneumatic tool, the air filter covers the entire sectional area of the air chamber within the grip. Therefore, the effective sectional area of the passage is reduced by the air filter, which in turn reduces the air supply rate of the compressed air supply port. As a result, the air pressure recovery time in the continuous operation of the pneumatic tool is increased to impair the operability of the tool.
Further, since the foreign matter entrapped by the air filter deposits within the air chamber between the air filter and the compressed air supply port, it is necessary to remove the end cap from the housing in order to eliminate the foreign matter, making the maintenance of the tool cumbersome.